I've had iPhones prior to my close to six months experience with the S4. Battery life is inversely proportional to one's screen brightness setting. It is definitely less than the iPhone's battery life with average, as well as, heavy use.
We can debate the two formats, ad nauseum, and can make cases for either platform. The reality is that there are definitely pros and cons of the Android format vs. IOS. A few of the Android pros are the greater ability to personalize, upgradable external memory, and the replaceable battery. If battery life is your main concern with Android, I don't think it's a big deal carrying around an extra battery during periods of heavier usage.